Anti-pressure system

ABSTRACT

An anti-pressure system for a vessel which is subject to internal pressure created by heating or boiling of its contents, the system including first and second spaced-apart outlets for vapor to exit the vessel, each outlet having a first side communicating with the vessel interior and a second side communicating with the vessel exterior. The invention provides a reliable method of protecting a normally un-pressurized vessel, such as an autoclave, distillation vessel, boiler or the like, from dangerous pressure build-up, resulting from its vapor outlet being blocked, regardless of what other pressure release devices, if any, may be present on the vessel.

FIELD OF THE INVENTION

The present invention relates generally to an anti-pressure system. Moreparticularly, the present invention relates to an anti-pressure systemfor a vessel which is subject to internal pressure created by heating orboiling of its contents.

BACKGROUND OF THE INVENTION

There are many examples of vessels wherein the contents are subjected toheating or boiling. Examples are autoclaves, distillation vessels,boilers, etc. With the exception of vessels such as pressure cookers,wherein pressure build-up is intentional and the vessel is constructedto withstand internal pressures, it is customary to provide an outletfor vapour generated during the boiling or distillation process. In suchcases, it is also desirable to provide a pressure relief means whichwill allow vapour to be vented from the vessel in the event that theinternal pressure rises to a dangerous level, caused by blockage of thevapour outlet. An example of a situation where such a blockage couldoccur is where the vessel has an internal liner, as may be the case witha distillation vessel. Such a liner may be in the form of a bag insidethe distillation vessel, as described in Canadian Patent Application No.2,277,449. The material to be processed—for example, used solvent from acleaning process—is placed in the bag and the vessel heated to drive offthe solvent vapour, which exits through an outlet to acondensation/collection vessel. In the event the outlet opening wouldever be blocked, for safety reasons there should be some kind ofanti-pressure device incorporated into the distillation vessel, such asan anti-pressure valve placed on the cover of the vessel to releasebefore any significant pressure build up can occur. In theaforementioned Canadian Patent Application No. 2,277,449 the coveritself was designed to release at almost any sign of positive pressure.However during field tests it was found that, in certain instances, thisanti-pressure device was not effective against a dangerous pressurebuild up and release. The cause was the bag being overfilled withsolvent, which overflowed behind the bag. As the vessel heated up, thesolvent behind or outside the bag began to vaporize and expand. As thevapour expanded, more liquid from inside the bag overfilled to theoutside of the bag, creating more vapour until the bag was pushedupwardly from underneath and eventually covered the vapour exit. Now,with the vapour exit blocked, the cover should have released, but didnot, as the bag being pushed from the inside out in a balloon effectpushing on the cover and eventually pushing the cover open could notrelease the pressure, because the bag itself was sealing the opening.The bag continued to expand inside the vessel until finally hot solventburst from the inside to the surrounding area. This, of course, is verydangerous and could occur in any container that has the possibility ofits normal vapour outlet and any pressure release device being blocked.

Hence there is a need for a more reliable method of protecting anormally un-pressurized vessel from dangerous pressure build up,resulting from its vapour outlet being blocked, regardless of what otherpressure release devices (if any) may be present on the vessel.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides an anti-pressuresystem for a vessel which is subject to internal pressure created byheating or boiling of its contents, the system comprising first andsecond spaced-apart outlets for vapour to exit the vessel, each outlethaving a first side communicating with the vessel interior and a secondside communicating with the vessel exterior.

Preferably, the first outlet is located above the second outlet and thesecond side of the first outlet communicates with the second side of thesecond outlet through a conduit extending downwardly from the secondside of the first outlet to the second side of the second outlet. Theconduit is preferably located within the vessel and is provided with aplurality of openings in a wall of the conduit to allow vapour from thevessel to enter the conduit through the openings and to exit the vesselthrough the second side of the first outlet. In a preferred embodiment,the conduit comprises a tube and in a further preferred embodiment, thesecond side of the first outlet is formed by an elbow communicating withthe vessel exterior and the tube communicates with and extendsdownwardly from the elbow. In an alternative preferred embodiment, theconduit is formed by an elongated shroud having the openings therein andsecured to an internal wall surface of the vessel. Preferably, theconduit extends downwardly adjacent an internal wall surface of thevessel and, where a liner or bag is used in the vessel, the conduitextends between the liner or bag and the internal wall surface of thevessel.

Alternatively, the second outlet communicates directly with the exteriorof the vessel. In the case where vapour exiting the vessel is suppliedby means of a first conduit to a condensation/collection vessel for thevapour, a second conduit may be provided either between the secondoutlet and the condensation/collection vessel or between the secondoutlet and the first conduit. A one-way valve may be provided to preventflow of vapour through the second conduit to the second outlet.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a sectional view of a distillation module of the typedescribed in our Canadian Patent Application No. 2,277,449;

FIG. 2 is a sectional view of the distillation module of FIG. 1, showingthe bag in its deformed condition;

FIG. 3 is a perspective view of an upper region of the distillationmodule of FIG. 1, showing an anti-pressure device according to oneembodiment of the invention;

FIG. 4 is a sectional view of the distillation vessel showing thepositional relationship between the bag and the anti-pressure device ofFIG. 3; and

FIG. 5 is a perspective view of the distillation vessel showing analternative form of the anti-pressure device according to the invention.

FIG. 6 is a detailed perspective view of another embodiment of thedistillation vessel in which the shroud extends over the vapour outlet;and

FIG. 7 is a side elevational view of an embodiment of the invention inwhich the shroud is replaced by a second vapour outlet.

DETAILED DESCRIPTION

FIG. 1 shows a distillation module [1] as used in the solvent vapourrecovery system described in Canadian Patent Application No. 2,277,449.The distillation module [1] comprises a distillation vessel [2] in whichcontaminated solvent or solvent mixture [S] to be recovered iscollected. The distillation vessel [2] is closed to prevent the escapeof any vapour generated therein other than through an outlet [12] havinga first side communicating with the vessel interior and a second sidecommunicating with the vessel exterior through a conduit [13], whichleads to a condensation/collection vessel (not shown). The sizes of theoutlet [12] and conduit [13] are made adequate to allow free passage ofvapour from the distillation vessel [2] without resulting in a pressurebuild up in the distillation vessel [2]. Further, the outlet [12] isideally positioned toward the upper end of the distillation vessel [2]since the hot vapour will rise. Heat is applied to the vessel [2] tovaporize the solvent and in the particular example shown in FIG. 1, itis applied by means of a larger heating vessel [3] containing an oilbath [5], within which the distillation vessel [2] sits. The heatingvessel [3] is provided with one or more heating elements [4] immersed inthe oil and, in operation, each heating element [4] heats the oil [5]which in turn heats the distillation vessel [2] at least until thesolvent [S] within the distillation vessel reaches its boiling point andvapour is generated. Once the boiling point of the solvent is reached,the power supplied to the heating element is controlled to regulate therate of vaporization of the solvent until the solvent is substantiallyall evaporated. Of course, it is not important to the present inventionwhat type of heating arrangement is employed and the foregoingarrangement is shown merely by way of illustration.

Continued heating of the distillation vessel drives off any residualsolvents and bakes any contaminants in the distillation vessel so thatthe resulting solids can be disposed of more conveniently at a lowercost and with reduced environmental problems as compared to unbakedcontaminants. Typically, the distillation vessel is lined with a bag [8]such that, following baking, the entire bag [8] containing the bakedcontaminants can be disposed of. The bag [8] is stable within thetemperature range of the distillation vessel [2] and is inert withrespect to the solvents to be distilled. The bag [8] is made of anysuitable material that is heat stable, does not react with the solventsto be distilled, and is non-permeable.

In the event that the outlet [12] used as the vapour outlet to thecooling system would ever be blocked, for safety reasons, some kind ofanti-pressure device is incorporated into the vessel lid or cover [14].Such device may be an anti-pressure valve placed on the cover of thevessel to release before any significant pressure build up can occur orthe cover itself may be designed to release at almost any sign ofpositive pressure. However, it has been found in certain instances thatanti-pressure devices incorporated into the vessel lid or cover are notalways effective to prevent dangerous pressure build up and release.

As noted above, the cause has been found to be that the distillation bagcan be overfilled and solvent can therefore overflow and accumulatebehind the bag. Under these conditions, as the vessel heats up, thesolvent behind or outside the bag begins to vaporize and expand. As thevapour expands, more liquid from inside the bag overflows to the outsideof the bag, creating more vapour between the bag and the vessel untilthe bag is deformed by being pushed upwards from underneath andeventually covers the vapour outlet [12] (see FIG. 2). Now with thevapour outlet blocked, the increasing pressure within the vessel shouldcause the anti-pressure device to release, but it may not do so in allcases as the bag being pushed from the inside out in a balloon effectpushing on the cover and eventually pushing the cover open prevents theanti-pressure device from releasing the pressure as the bag itself canseal the opening. The bag can continue to expand outside the vesseluntil finally hot solvent from the inside bursts over the surroundingarea.

Another possible source of blockage, which can occur even when a lineris not present, is sludge from the used solvent which could block theoutlet if insufficient care is used in pouring the used solvent into thevessel.

To solve this problem, the inventors have provided a means wherebyvapour is still able to exit the vessel, regardless of any overflow fromthe bag or sludge blockage of the vapour outlet [12] and consequentpressure build-up as described above. Referring to FIGS. 3 and 4, in apreferred embodiment of the invention, the anti-pressure device of theinvention comprises an elbow [20] (typically three quarter inch)attached to the outlet [12] for vapour escape. Thus, the vapour outlet[12 a] is now formed by the entrance to the elbow and the elbow becomesthe second side of the vapour outlet [12 a]. A hole is provided in thebottom of the elbow, and is attached to a tube [21] forming a conduitextending downwardly adjacent the vessel wall, to the bottom of thevessel. The tube has holes [22] from top to bottom acting as a pluralityof possible exits for vapour, each having a first side communicatingwith the vessel interior and a second side communicating through theelbow [20] with the vessel exterior. Therefore, if one hole is blockedby the bag, another is always open. Alternatively, as shown in FIG. 5,the conduit may be formed by a shroud [24] attached to the vessel walland communicating with the elbow [20].

In a further embodiment as shown in FIG. 6, the shroud [24] extends overthe vapour outlet. The shroud is made of angle iron with holes [22]along its entire length, extending from top to bottom along the side ofthe vessel from top to bottom of the vessel. Again, the plurality ofholes in the shroud ensures that the vapour always has an unobstructedexit path from the vessel, through the second side of the vapour outlet.Whether the conduit for the vapour is formed by a tube or a shroud asdescribed above, it is important that when using it in conjunction witha distillation bag, the conduit be located outside the bag as shown inFIG. 4, so as to ensure no pressure build up can occur from outsideand/or under the bag.

In yet a further embodiment, as shown in FIG. 7, the tube or shroud maybe dispensed with entirely and replaced by a second vapour outlet [25],spaced from the outlet [12], the second side of the outlet [25]communicating with an external conduit [26]. Conduit [26] can beconnected (preferably through a one-way valve [27] to prevent reverseflow of vapour from the conduit [26] to the second outlet [25]) eitherto the first conduit [13] for vapour exiting through the outlet [12] ordirectly with the condensation/collection vessel.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

1. An apparatus used in the distillation of materials, said apparatuscomprising a vessel, a bag within the interior of said vessel forcontaining said materials, said vessel having an internal wall surfaceand an outlet for vapor to exit said vessel from the distillation ofsaid materials, an anti-pressure system for said vessel, saidanti-pressure system wherein said outlet has a first side communicatingwith said vessel interior and a second side communicating with theexterior of said vessel, a conduit extending downwardly into said vesseladjacent said internal wall surface of said vessel and between said bagand said internal wall surface, said conduit communicating with saidsecond side of said outlet, said conduit having at least one opening incommunication with said vessel interior to allow vapor from said vesselto enter said conduit through said opening and to exit said vesselthrough said second side of said outlet, said conduit being formed by anelongated shroud secured to an internal wall surface of said vessel,said second side of said outlet formed by an elbow communicating withsaid vessel exterior and said conduit communicating with and extendingdownwardly from said elbow.
 2. The combination of claim 1 wherein saidconduit opening is located along said internal wall surface of saidvessel.
 3. The combination of claim 2 wherein said conduit includes aplurality of openings located along said internal wall surface.